1. Field of the Invention
The present invention relates to a roving bobbin changing method and apparatus for a spinning machine in which the roving bobbins changing operation is carried out by a roving bobbin changing apparatus which is adapted to move along a longitudinal axis of the spinning machine from one end of the machine frame toward the other end thereof.
2. Description of the Related Art
In the spinning machine typified by a ring spinning machine among others, rovings are drawn out from roving bobbins suspended on a creel of the spinning machine to be delivered to a draft part disposed below the creel. When the roving bobbins become empty or approach the empty state as the roving delivering to the draft part progresses, there arises a need for exchanging the empty or nearly empty roving bobbins (hereinafter referred to as the roving-depleted bobbins) with new or full roving bobbins. In that case, ends of the rovings drawn out from the full roving bobbins have to be connected or tied to the rovings being delivered from the roving-depleted bobbins or alternatively the rovings of the full roving bobbins must be inserted into the draft part.
In an effort to reduce the manpower involved in the spinning process, there has already been proposed a roving bobbin changing method (or sliver changing method) according to which the roving tying operation and the roving bobbin changing operation are carried out sequentially and progressively from one end of the machine frame of the spinning machine toward the other end thereof. By way of example, according to a roving bobbin changing method disclosed in Japanese Unexamined Patent Application Publication No. 57478/1988 (JP-A-63-57478), a roving bobbin changing apparatus performs an operation for finding and picking up roving ends from full roving bobbins (stocked full roving bobbins) and an operation for tying or connecting the roving ends as picked up to the rovings being delivered for spinning at the same positions. Thereafter the roving bobbin changing apparatus is moved to another position or work station where a next roving tying operation is to be carried out. Through the first mentioned operation, the roving-depleted bobbins are transferred to bobbin hangers suspended on the auxiliary rail, while the full roving bobbins are suspended on the bobbin hangers mounted on the creel of the spinning machine (this operation will be referred to as the roving bobbin exchanging operation) after the roving tying operation. In the meanwhile, the roving end finding/pick-up operation and the roving tying operation are carried out for the full roving bobbins.
According to the scheme disclosed in Japanese Unexamined Patent Application Publication No. 127368/1990 (JP-A-H2-127368), a work section for the roving bobbin changing operation is divided into three subsections, i.e., a roving end finding/pick-up section, a roving tying section, and a roving bobbin exchanging section. These three sections are sequentially disposed in tandem in the direction in which the roving bobbin changing apparatus is moved for performing the roving bobbin exchanging operation, and the operations in the individual work sections are carried out substantially concurrently with one another. More specifically, in the roving end finding/pick-up section, the roving ends are found and picked up from at least two full roving bobbins suspended on an auxiliary rail, while in the roving tying section the roving ends of the full roving bobbins as found and picked up are tied to the rovings being delivered from a pair of roving-depleted bobbins disposed in sequence. In the roving bobbin exchanging section, the pair of roving-depleted bobbins are transferred to the auxiliary rail after the roving tying operation, while the full roving bobbins which are now delivering the rovings are transferred to bobbin hangers mounted on the lower surface of the creel.
In recent years, there has arisen a prominent trend for increasing the operational speed of the spinning machine with a view to enhancing productivity. In accompaniment with the high-speed spinning, the diameter of the yarn-wound spool (or cop, to say in other way) has been reduced by controlling ballooning during the spinning operation in order to ensure a high quality of yarn. Under these circumstances, the cop change cycle becomes remarkably shortened. On the other hand, in view of the demand for manufacturing yarn at low costs, the spinning machine of low power consumption type which is equipped with a large number of spindles (on the order of 1,000 spindles) is increasingly used. This type spinning machine has a machine frame which is at least twice as long as that of the conventional spinning machine. Besides, there exists a necessity for carrying out the exchange of roving bobbins during operation of the spinning machine in order to prevent the manufacturing efficiency of the spinning machine from being reduced.
In this connection, the roving tying operation is realized by placing end portions of rovings picked up from full roving bobbins on rovings being delivered from roving-depleted bobbins over only a short length, and bonding together both rovings at a location immediately before the back rollers. Consequently, the bonded or tied portions of the rovings have an increased diameter, which often results in an undesirable situation in that the balloon is enlarged upon reception of the bonded or tied roving portions fed through front rollers, involving a high possibility of yarn breakage. Of course, when the cop has grown to a diameter in the range of from fifty to seventy percent of a full cop, yarn breakage becomes difficult to take place because the ballooning is then less significant as the distance between the snail wire, anti-node ring and the traveller is decreased. For this reason, in order to prevent the manufacturing efficiency from lowering by preventing the yarn breakage after the roving tying, it is necessary to start the roving bobbin changing operation when the cop diameter has increased up to a range of from fifty to seventy percent of the finished diameter. However, starting of the roving bobbin changing operation with the aid of a roving bobbin changing apparatus at a time when the cop has reached the diameter mentioned above is accompanied by the problem that the cop may become full before the roving bobbin changing operation has been completed for all the roving bobbins in a spinning machine if a lot of time is taken for the roving bobbin exchanging process. This may result in stoppage of the spinning machine and interference between the roving bobbin changing apparatus and the cop changer. Thus, there exists a need for a high speed roving bobbin exchanging facility in order to meet a demand for preventing the above-mentioned interference and increasing the number of spinning machines to be serviced by a single roving bobbin changing apparatus.
According to the roving bobbin changing method described in Japanese Unexamined Patent Application Publication No. 57478/1988 (JP-A-63-57478), the roving end finding/pick-up operation and the roving tying operation are effected at one and the same location and, after completion of the roving tying operation, the roving bobbin changing apparatus is moved to a succeeding roving tying position to thereby carry out the roving tying operation with the roving bobbin changing operation being carried out concurrently at the same position. However, the roving end finding/pick-up operation and the roving tying operation require a longer time when compared with the time taken by the roving bobbin-changing operation. Consequently, even when one cycle of the roving bobbin changing process is performed almost concurrently, the relatively long time required for completing the roving end finding/pick-up operation and the roving tying operation in one cycle provides an obstacle in realizing a reduction in the time for the roving bobbin changing apparatus to stay at one and the same place. As a result, the time required for completing the roving bobbin changing process for the whole spinning machine is unavoidably increased, giving rise to a problem.
On the other hand, in the case of the roving bobbin changing scheme taught in Japanese Unexamined Patent Application Publication No. 127368/1990 (JP-A-H2-127368) mentioned previously, the work section for a roving bobbin changer is divided into three subsections, i.e. a roving end finding/pick-up section, a roving tying section, and a roving bobbin exchanging section, and the relevant operations are performed concurrently. As a consequence, the time for the roving bobbin changing apparatus to stay at one place can be reduced, whereby the time required for completing the roving bobbin changing operation for a whole spinning machine can significantly be shortened. However, this prior art roving bobbin changing scheme suffers from a problem that the control becomes much more complicated because of the large number of work sections to be monitored. Besides, upon occurrence of a trouble in a given one of the sections in the course of performing the allocated operation, the apparatus has to be restored to the original position, whereupon the roving bobbin changing process is started again, which thus incurs a problem that the burden imposed on the operator who is in charge of monitoring and controlling the roving bobbin changing process will intolerably be increased.
Such being the circumstances, there exists a great demand for a roving bobbin changing method and apparatus which allows the time taken for the roving bobbin changing operation for one spinning machine to be significantly shortened without involving complication in the control of the roving bobbin changing apparatus or increasing the burden imposed on the operator.